Unless otherwise indicated herein, the information described in this section is not prior art to the claims and is not admitted to be prior art by inclusion in this section.
In some wireless communication systems, when data that is transmitted by a transmitting entity to a receiving entity is not received by the receiving entity, or is received by the receiving entity with one or more errors, the data may be re-transmitted. The re-transmission of data could occur either automatically or in response to feedback from the receiving entity. For example, in Long Term Evolution (LTE) systems and in other systems, a Hybrid Automatic Repeat Request (HARQ) procedure is used. In the HARQ approach, after a transmitting entity has transmitted a block of data, the transmitting entity waits to receive an HARQ response from the receiving entity. If the transmitting entity receives a positive acknowledgement (ACK) as the HARQ response, then no re-transmission is needed and the transmitting entity can transmit additional data. If the transmitting entity receives a negative acknowledgement (NACK) as the HARQ response, then the transmitting entity re-transmits the data. The transmitting entity may also re-transmit the data if the transmitting entity does not receive any HARQ response within a certain period of time.
This re-transmission approach can allow data to be successfully transmitted from a transmitting entity to a receiving entity even when there is a substantial probability that the transmitted data will be received with one or more errors, for example, because of poor radio frequency (RF) conditions. Specifically, the data can be re-transmitted multiple times until the data is received without errors. This re-transmission approach, however, also increases latency. For example, there can be a period of delay between when the transmitting entity transmits data and when the transmitting entity receives a NACK response from the receiving entity and another period of delay between when the transmitting entity receives the NACK response and when the transmitting entity begins re-transmitting the data.
In order to reduce the delay associated with re-transmitting data, LTE supports a bundling option for data transmissions by a user equipment device (UE) in the Physical Uplink Shared Channel (PUSCH). Normally, a UE transmits data in one transmission time interval (TTI), which corresponds to a 1 millisecond (ms) subframe, and then waits to receive an HARQ response before re-transmitting the data or transmitting additional data. However, when TTI bundling is used, the UE transmits the same data repeatedly in two, three, or four consecutive TTIs (possibly varying each of these repeated transmissions by including different error correction coding in or with each one) and then waits to receive an HARQ response. This transmission of multiple instances of the same data (or substantially the same data) may consume a greater extent of PUSCH resources up front, but can allow for more robust reception of the data, without the delay that would be associated with the UE transmitting the data multiple times and waiting for an HARQ response after each transmission.